Just 3 days ago I got a package from Brent Jesse. It contained the 1960s Mazda ladder plates 12AU7 for my Backert Labs Rhumba. I installed them and kept the preamp ON for 2 hours and sat down for a serious auditioning. I am not going to say "blow out of water" or "I was blown away", etc etc, lest I jinx them. All I will say is that comparing the Mazdas to the Psvane ART series tubes is like comparing a 23 year old man/woman with a 40+ man/woman respectively. Hope you get it. I was told that they need at least 48 hours to sound nice. They sound nice right now. I am not going to keep them ON for a long time just to let them "burn in".
Yes, the Mazdas are pricey, but they are keepers. Mind you, the Psvane ART series are not bad at all. In fact of all the current production tubes, they are THE BEST. Only after listening to the Mazdas, did I realize that the Psvanes produce excess bass that is a bit bloated. The Mazda bass is very tight. Also the Psvanes do not extend and light up the treble the way the Mazda does.